【POJ 2362】【検索】Square

#include "iostream"
#include "algorithm"
using namespace std;
int a[100],vis[100];
int n,len,flag;
void dfs(int num,int ans,int k);
int main(int argc, char const *argv[])
{
  int t;
  scanf("%d",&t);
  while(t--)
  {
    int sum=0;
    scanf("%d",&n);
    for (int i = 0; i < n; ++i)
    {
      scanf("%d",&a[i]);
      sum+=a[i];
    }
    if(sum%4==0)
    {
      sort(a,a+n);
      memset(vis,0,sizeof(vis));
      flag=0;
      len=sum/4;
      dfs(0,0,0);
      flag?printf("yes
"):printf("no
");
    }
    printf("no
");
  }
  return 0;
}
void dfs(int num,int ans,int k)
{
  if(num==3)//      ，      ，           ，    
  {
    flag=1;return;
  }
  if(ans==len)
  {
    num++;
    k=0;
    ans=0;
  }
  for (int i = k; i < n; ++i)
  {
    if(!vis[i] && ans+a[i]<=len)
    {
      vis[i]=1;
      dfs(num,ans+a[i],i+1);
      if(flag)
        return;
      vis[i]=0;
    }
  }
}